Hydrogen storage materials for hydrogen and energy carriers

Hydrogen storage technology is essentially necessary to promote renewable energy. Many kinds of hydrogen storage materials, which are hydrogen storage alloys, inorganic chemical hydrides, carbon materials and liquid hydrides have been studied. In those materials, ammonia (NH₃) is easily liquefied by compression at 1 MPa and 298 K, and has a highest volumetric hydrogen density of 10.7 kg H₂/100 L. It also has a high gravimetric hydrogen density of 17.8 wt%. The theoretical hydrogen conversion efficiency is about 90%. NH₃ is burnable without emission of CO₂ and has advantages as hydrogen and energy carriers.     

Recent progress towards solar energy integration into low-pressure green ammonia production technologies

Large progress has been made in the last decades to reduce the carbon footprint of ammonia, which is an essential commodity of the food, chemical and energy industry. Apart from alternative routes for green feedstock production, such as hydrogen via electrolysis and nitrogen via solar thermochemical methods, alternatives are explored to replace the Haber-Bosch process. The present article reviews four promising mild condition ammonia production methods: solid state synthesis, molten salt synthesis, thermochemical looping and photocatalytic routes. Contrary to the Haber-Bosch method, which requires high pressures of 200–400 bar, they operate at low-pressures, furthermore such routes open the possibility for direct ammonia production from H₂O and N₂ without the intermediate hydrogen production step. These advantages allow easier renewable energy integration; however, R&D activities are needed for scaling-up. An analysis is given on renewable energy integration with focus on solar resources both in the form of electricity and heat.     

The enhancement of magnetic field assisted water electrolysis hydrogen production from the compact disc recordable waste polycarbonate layer

E-waste is growing rapidly in today's data technology era while the need for green energy is critical. Current compact disc recordable (CD-R) e-waste utilization for hydrogen production by electrolysis is still classified as gray hydrogen production. This study aims to synthesize electrocatalyst for green hydrogen production from CD-R polycarbonate layer. The elemental and morphological characterizations were performed in this study along with molecular dynamics simulation and direct electrolysis experiment. The electrolysis test results shows EMF and high Bisphenol-A (BPA) content from 3 g polycarbonate produce 26000 ppm H₂ almost tripled the EMF only with 10000 ppm H₂ and doubled the EMF with 1 g polycarbonate 15000 ppm H₂. EMF and BPA cooperatively reduces water ionization energy through diamagnetic response and aromatic resonance which vibrates water molecule. Following that, the EMF slowed down OH⁻ ion movement causes the H⁺ movement towards electron become unrestricted. In conclusion, the EMF-BPA cooperation increases hydrogen evolution reaction (HER) through water ionization energy reduction and ion transfer modification.     

Hydrogen as an export commodity – Capital expenditure and energy evaluation of hydrogen carriers

In this paper, we describe a case-study exploring the use of 600 MW of power from New Zealand's Manapouri Power Station to produce hydrogen for export via water electrolysis. Three H₂ carriers were considered: liquid H₂, ammonia, and toluene hydrogenation/methylcyclohexane dehydrogenation. Processes were simulated in Aspen's HYSYS for each of the carriers to determine their associated energy and annualised capital expenditure costs. We found that the total capital investment for all carriers was surprisingly consistent, but with quite different splits between the electrolysis and carrier formation plants. Based on our analysis the energy availability for liquid H₂ ranged from 53.9 to 60.7% depending on the energy cost associated with cryogenic H₂ liquefaction. The energy availability for liquid ammonia was 37.5% after conversion back to H₂, or 53.6% if the ammonia can be used directly as a fuel. For toluene/methylcyclohexane the energy availability was 41.2%. The total of the electricity and annualised capital costs per kg of H₂ ranged from NZ$5.63 to NZ$6.43 for liquid H₂, NZ$6.24 to NZ$8.91 for ammonia and was NZ$7.86 for toluene/methylcyclohexane, using a net electricity cost of NZ$70/MWh. The cost of hydrogen (or energy in the case of direct use ammonia) was more strongly influenced by the efficiency of energy retention than on capital investment, as the electricity costs contributed approximately two thirds of total costs. In the long-term, liquid hydrogen looks to be the most versatile H₂ carrier, but significant infrastructure investment is required.     

Beyond Haber-Bosch: The renaissance of the Claude process

Ammonia may be one of the energy carriers in the hydrogen economy. Although research has mostly focused on electrochemical ammonia synthesis, this however remains a scientific challenge. In the current article, we discuss the feasibility of single-pass thermochemical ammonia synthesis as an alternative to the high-temperature, high-pressure Haber-Bosch synthesis loop. We provide an overview of recently developed low temperature ammonia synthesis catalysts, as well as an overview of solid ammonia sorbents. We show that the low temperature, low pressure single-pass ammonia synthesis process can produce ammonia at a lower cost than the Haber-Bosch synthesis loop for small-scale ammonia synthesis (<40 t-NH₃ d^?1).     

On-board hydrogen storage and production: An application of ammonia electrolysis

On-board hydrogen storage and production via ammonia electrolysis was evaluated to determine whether the process was feasible using galvanostatic studies between an ammonia electrolytic cell (AEC) and a breathable proton exchange membrane fuel cell (PEMFC). Hydrogen-dense liquid ammonia stored at ambient temperature and pressure is an excellent source for hydrogen storage. This hydrogen is released from ammonia through electrolysis, which theoretically consumes 95% less energy than water electrolysis; 1.55 Wh g⁻¹ H₂ is required for ammonia electrolysis and 33 Wh g⁻¹ H₂ for water electrolysis. An ammonia electrolytic cell (AEC), comprised of carbon fiber paper (CFP) electrodes supported by Ti foil and deposited with Pt-Ir, was designed and constructed for electrolyzing an alkaline ammonia solution. Hydrogen from the cathode compartment of the AEC was fed to a polymer exchange membrane fuel cell (PEMFC). In terms of electric energy, input to the AEC was less than the output from the PEMFC yielding net electrical energies as high as 9.7 ± 1.1 Wh g⁻¹ H₂ while maintaining H₂ production equivalent to consumption.     

Liquid hydrogen,methylcyclohexane, and ammonia as potential hydrogen storage: Comparison review

Among the several candidates of hydrogen (H₂) storage, liquid H₂, methylcyclohexane (MCH), and ammonia (NH₃) are considered as potential hydrogen carriers, especially in Japan, in terms of their characteristics, application feasibility, and economic performance. In addition, as the main mover in the introduction of H₂, Japan has focused on the storage of H₂, which can be categorized into these three methods. Each of them has advantages and disadvantages compared to the other. Liquid H₂ faces challenges in the huge energy consumption that occurs during liquefaction and in the loss of H₂ through boil-off during storage. MCH has its main obstacles in requiring a large amount of energy in dehydrogenation. Finally, NH₃ encounters high energy demand in both synthesis and decomposition (if required). In terms of energy efficiency, NH₃ is predicted to have the highest total energy efficiency, followed by liquid H₂, and MCH. In addition, from the calculation of cost, NH₃ with direct utilization (without decomposition) is considered to have the highest feasibility for massive adoption, as it shows the lowest cost (20–22 JPY·Nm³-H₂ in 2050), which is close to the government target of H₂ cost (20 JPY·Nm³-H₂ in 2050). However, in the case that highly pure H₂ (such as for fuel cell) is needed, liquid H₂ looks to be promising (24–25 JPY·Nm³-H₂ in 2050), compared with MCH and NH₃ with decomposition and purification.     

Wind-powered 250 kW electrolyzer for dynamic hydrogen production: A pilot study

Alkaline water electrolysis is the most promising approach for the industrial production of green hydrogen. This study investigates the dynamic operational characteristics of an industrial-scale alkaline electrolyzer with a rated hydrogen production of 50 m³/h. Strategies for system control and equipment improvement in dynamic-mode alkaline electrolytic hydrogen production are discussed. The electrolyzer can operate over a 30%–100% rated power load, thereby facilitating high-purity (>99.5%) H₂ production, competitive DC energy efficiency (4.01–4.51 kW h/Nm³ H₂, i.e., 73.1%–65.0% LHV), and good gas–liquid fluid balance. A safe H₂ content of 2% in O₂ (50% LFL) can be guaranteed by adjusting the system pressure. In transient operation, the electrolyzer can realize minute-level power and pressure modulation with high accuracy. The results confirm that the proposed alkaline electrolyzer can absorb highly fluctuating energy output from renewables because of its capability to operate in a dynamic mode.     

Green hydrogen-based pathways and alternatives: Towards the renewable energy transition in South America's regions–Part B

Hydropower compounds most of the energy matrix of the countries of the Latin America and Caribbean region (LAC). Considering the concern in reducing Green House Gases emissions (GHG) from hydropower plants and hydrogen production from fossil sources, green hydrogen (H₂) appears as an energy vector able to mitigate this impact. Improving the efficiency of the plant and producing renewable energy the element is an interesting alternative from the ecological and economic point of view. This study aims to estimate the potential of H₂ production from wasted energy, through the electrolysis of water in hydroelectric plants in Colombia and Venezuela. The construction of two scenarios allowed obtaining a difference, considering a spilled flow of 2/3 in the first scenario and 1/3 in the second. In Colombia, hydrogen production reached 3.39 E+08 Nm³ at a cost of 2.05 E+05 USD/kWh in scenario1, and 1.70 E+08 Nm³ costing 4.10 E+05 USD/kWh in scenario 2. Regarding the Venezuelan context, the country obtained lower production values of H₂, ranging between 7.76 E+07 Nm³.d^?1 and 4.31 E+07 Nm³.d^?1, and production cost between 9.45 E+09 USD/kWh and 1.89 E+10 USD/kWh. Thus, the final cost for the production and storage of H₂ was estimated at 0.2239 USD.kg^?1. Ultimately, Colombia and Venezuela have a large potential to supply the demand for nitrogen fertilizers with green ammonia production, apply green hydrogen in manufacturing and use the surplus for energy substitution of Liquefied Petroleum Gas - LPG. In Colombia, the chemical energy offered is equivalent to 6.681 E+11 MJ/year^?1 and in Venezuela, the result is equal to 1.697 E+11 MJ/year^?1 in the conservative scenario. Finally, the countries have great potential for the diversification of the energy matrix and the insertion of renewables in the system.     

Hydrogen generation from the dehydrogenation of ammonia–borane in the presence of ruthenium(III) acetylacetonate forming a homogeneous catalyst

Starting with ruthenium(III) acetylacetonate a homogeneous catalyst is formed which catalyzes the release of 1 equivalent of hydrogen gas from the dehydrogenation of ammonia–borane in toluene solution at low temperature in the range 50–65 °C. Mercury poisoning experiments showed that the catalytic dehydrogenation of ammonia–borane starting with ruthenium(III) acetylacetonate is a homogeneous catalysis. The final product obtained after the catalytic dehydrogenation of ammonia borane was thoroughly characterized by using ¹¹B Nuclear Magnetic Resonance and Infrared spectroscopies. The homogeneous catalyst formed from the reduction of ruthenium(III) acetylacetonate provides 950 turnovers (TTO) over 58 h and 27 (mol H₂)(mol Ru)⁻¹(h)⁻¹ value of initial turnover frequency (TOF) in hydrogen generation from the dehydrogenation of ammonia–borane at 60 °C before deactivation. Kinetics of this homogenous catalytic dehydrogenation of ammonia–borane was studied depending on the catalyst concentration, substrate concentration, and temperature. The hydrogen generation was found to be first order with respect to both the substrate concentration and catalyst concentration. The activation parameters of this reaction were also determined from the evaluation of the kinetic data: activation energy; E_a = 48 ± 2 kJ mol⁻¹, the enthalpy of activation; ΔH^# = 45 ± 2 kJ mol⁻¹ and the entropy of activation ΔS^# = −152 ± 5 J mol⁻¹ K⁻¹.     

Assessment of biotic and abiotic graphite cathodes for hydrogen production in microbial electrolysis cells

Hydrogen represents a promising clean fuel for future applications. The biocathode of a two-chambered microbial electrolysis cell (biotic MEC) was studied and compared with an abiotic cathode (abiotic MEC) in order to assess the influence of naturally selected microorganisms for hydrogen production in a wide range of cathode potentials (from −400 to −1800 mV vs SHE). Hydrogen production in both MECs increased when cathode potential was decreased. Microorganisms present in the biotic MEC were identified as Hoeflea sp. and Aquiflexum sp. Supplied energy was utilized more efficiently in the biotic MEC than in the abiotic, obtaining higher hydrogen production respect to energy consumption. At −1000 mV biotic MEC produced 0.89 ± 0.10 m³ H₂ d⁻¹ m⁻³NCC (Net Cathodic Compartment) at a minimum operational cost of 3.2 USD kg⁻¹ H₂. This cost is lower than the estimated market value for hydrogen (6 USD kg⁻¹ H₂).     

Life cycle CO2 emissions from power generation using hydrogen energy carriers

Hydrogen energy carriers such as liquid hydrogen (LH₂), methylcyclohexane (MCH), and ammonia (NH₃) are promising energy vectors in the clean energy systems currently being developed. However, their effectiveness in mitigating environmental emissions must be assessed by life cycle analyses throughout the supply chain. In this study, while focusing on hydrogen energy carriers, life cycle inventory analyses were conducted to estimate CO₂ emissions from the following types of power generation plants in Japan: a hydrogen (H₂) mono-firing power plant using LH₂ or MCH that originated from overseas renewable electricity; and NH₃ co-firing with fossil fuel and NH₃ mono-firing power plants using hydrogen energy carriers that originated from overseas natural gas or renewable electricity. Parameters related to the supply chains were collected by literature surveys, and the Japanese life cycle inventory database was primarily used to calculate the emissions. From the results, CO₂ hotspots of the target supply chains and potential measures are identified that become necessary to establish low-carbon supply chains.     

Large-scale decomposition of green ammonia for pure hydrogen production

It is acknowledged that Hydrogen has a decisive role to play in insuring a reliable and efficient penetration of renewable electricity in the energy mix. Nonetheless, building a sustainable Hydrogen Economy is faced with numerous challenges across the value chain. Namely, large-scale production and storage are still open issues that need to be addressed. A promising solution is to store renewable H₂ in the form of green ammonia often referred to as Power-to-Ammonia. Thus unlocking all available infrastructure for ammonia to effectively store and export hydrogen in bulk. In this value chain, the missing link is ammonia cracking to recover back hydrogen at high purities. The present work explores a technical solution to recover hydrogen from ammonia at large-scale. Through an exhaustive technoeconomic analysis, we have demonstrated the feasibility of large-scale production of pure H₂ from ammonia. The designed Ammonia-to-H₂ plant operates at a thermal efficiency of 68.5% to produce 200 MTPD of pure hydrogen at 250 bar. Furthermore, this study has established a final estimation of the Levelized Cost of Hydrogen (LCOH) from green ammonia. It was revealed that LCOH is mostly dependent on green ammonia cost, which in turn varies with renewable electricity cost.     

Wet-air co-electrolysis in high-temperature solid oxide electrolysis cell for production of ammonia feedstock

To significantly abate the carbon footprint in the conventional Haber-Bosch process, a novel approach based on wet air co-electrolysis in solid oxide electrolysis cell (SOEC) was proposed and evaluated in this study for sustainable single-step production of ammonia feedstock (i.e., H₂/N₂ mixture). An electrolyte-supported SOEC composed of LSCM-GDC cathode, SSZ electrolyte and LSCF-GDC anode was prepared and tested under various operation conditions. The current-voltage responses measured for wet air co-electrolysis were featured with three different regions which could be attributed to competitive and combinative effects of oxygen splitting reaction and water splitting reaction under wet air co-electrolysis operation. Gas chromatography (GC) analysis of the exit gas from the cathode chamber proved that high purity H₂/N₂ mixture had been produced successfully through the novel wet air co-electrolysis process. However, the obtained H₂:N₂ ratios were still much lower than the desired 3:1 ratio in the ammonia feedstock for the Haber-Bosch process. Further explorations will be made to increase the H₂:N₂ ratio in the produced gas mixture.     

On-board and Off-board performance of hydrogen storage options for light-duty vehicles

Leading physical and materials-based hydrogen storage options are evaluated for their potential to meet the vehicular targets for gravimetric and volumetric capacity, cost, efficiency, durability and operability, fuel purity, and environmental health and safety. Our analyses show that hydrogen stored as a compressed gas at 350–700 bar in Type III or Type IV tanks cannot meet the near-term volumetric target of 28 g/L. The problems of dormancy and hydrogen loss with conventional liquid H₂ storage can be mitigated by deploying pressure-bearing insulated tanks. Alane (AlH₃) is an attractive hydrogen carrier if it can be prepared and used as a slurry with >50% solids loading and an appropriate volume-exchange tank is developed. Regenerating AlH₃ is a major problem, however, since it is metastable and it cannot be directly formed by reacting the spent Al with H₂. We have evaluated two sorption-based hydrogen storage systems, one using AX-21, a high surface-area superactivated carbon, and the other using MOF-177, a metal-organic framework material. Releasing hydrogen by hydrolysis of sodium borohydride presents difficult chemical, thermal and water management issues, and regenerating NaBH₄ by converting B–O bonds is energy intensive. We have evaluated the option of using organic liquid carriers, such as n-ethylcarbazole, which can be dehydrogenated thermolytically on-board a vehicle and rehydrogenated efficiently in a central plant by established methods and processes. While ammonia borane has a high hydrogen content, a solvent that keeps it in a liquid state needs to be found, and developing an AB regeneration scheme that is practical, economical and efficient remains a major challenge.     

Large-scale long-distance land-based hydrogen transportation systems: A comparative techno-economic and greenhouse gas emission assessment

Interest in hydrogen as an energy carrier is growing as countries look to reduce greenhouse gas (GHG) emissions in hard-to-abate sectors. Previous works have focused on hydrogen production, well-to-wheel analysis of fuel cell vehicles, and vehicle refuelling costs and emissions. These studies use high-level estimates for the hydrogen transportation systems that lack sufficient granularity for techno-economic and GHG emissions analysis. In this work, we assess and compare the unit costs and emission footprints (direct and indirect) of 32 systems for hydrogen transportation. Process-based models were used to examine the transportation of pure hydrogen (hydrogen pipeline and truck transport of gaseous and liquified hydrogen), hydrogen-natural gas blends (pipeline), ammonia (pipeline), and liquid organic hydrogen carriers (pipeline and rail). We used sensitivity and uncertainty analyses to determine the parameters impacting the cost and emission estimates. At 1000 km, the pure hydrogen pipelines have a levelized cost of $0.66/kg H₂ and a GHG footprint of 595 gCO₂eq/kg H₂. At 1000 km, ammonia, liquid organic hydrogen carrier, and truck transport scenarios are more than twice as expensive as pure hydrogen pipeline and hythane, and more than 1.5 times as expensive at 3000 km. The GHG emission footprints of pure hydrogen pipeline transport and ammonia transport are comparable, whereas all other transport systems are more than twice as high. These results may be informative for government agencies developing policies around clean hydrogen internationally.     

Analysis of MTH-System (Methylcyclohexane-Toluene-Hydrogen-System) for hydrogen production as fuel for power plants

The utilization of hydrogen (H₂) gas as green energy fuel in power plants is a great challenge due to its storage, deployment and transportation. Herein, we propose a simulation based study of H₂ fueled power plant by using Methylcyclohexane-Toluene-Hydrogen-System (MTH-System). A 266 MW gas turbine was selected and the performance of MTH-System for power plant was investigated. The process for methylcyclohexane (MCH) production was not discussed here. However, the conversion of MCH into gaseous H₂ for power generation was discussed in detail. A sustainable process flow diagram (PFD) was developed. The heat integration b/w power plant and dehydrogenation reactor reveal that, minimum 70% MCH conversion is required to accomplish the heat demand of whole system. The effect of addition of H₂ recycle stream to dehydrogenation reactor and combined cycle power plants was investigated. The sensitivity and economic analysis reveal 2291.4 $/kW capital cost based on dehydrogenation of MCH for power production and 0.186 $/kWh output electricity cost based on complete MTH-System.     

Equilibrium shift of methylcyclohexane dehydrogenation in a thermally stable organosilica membrane reactor for high-purity hydrogen production

A high-performance organosilica membrane was prepared via sol–gel processing for use in methylcyclohexane (MCH) dehydrogenation to produce high-purity hydrogen. The membrane showed a high H₂ permeance of 1.29 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹, with extremely high H₂/C₃H₈ and H₂/SF₆ selectivities of 6680 and 48,900, respectively, at 200 °C. The extraction of hydrogen from the membrane reactor led to the MCH conversion higher than the thermodynamic equilibrium, with almost pure hydrogen obtained in the permeate stream without considering the effect of carrier gas and sweep gas in the membrane reactor, and the organosilica membrane reactor was very stable under the reaction conditions employed.     

Highly selective and efficient ammonia synthesis from N2 and H2O via an iron-based electrolytic-chemical cycle

Ammonia production via electroreduction of N₂ and water under mild conditions is emerging as a promising alternative to the fossil fuels-reliance and CO₂ emitting Haber-Bosch process. However, the achievement of high Faradaic efficiency and high ammonia formation rate is still challenging. Here, we demonstrate how ammonia can be selectively produced from N₂ and H₂O via a two-step iron-based cyclic process using a molten hydroxide electrolyte. The first step is the production of Fe by electrochemical reduction of Fe₂O₃. The second step is the steam-hydrolysis of Fe with bubbling N₂ to produce NH₃ and reform Fe₂O₃. Both reaction steps proceed isothermally at 250 °C in a molten salt electrolytic cell without switching of temperature and needing separation of the mediator, resulting in more easily putting into industrial practice. The cycle achieves an ultrahigh Faradaic efficiency of 79.8% at 1.15 V and a high ammonia formation rate of 1.34 × 10⁻⁸ mol s⁻¹ cm⁻² at 1.75 V. This is a critical advance in breaking the domination of hydrogen evolution reaction (HER) competition to achieve highly selective and efficient NH₃ synthesis from N₂ and H₂O beyond reliance of fossil fuels.     

Thermodynamic analysis of novel vanadium redox materials for solar thermochemical ammonia synthesis from N2 and CH4

Owing to the wide applications of ammonia in hydrogen field and high energy consumption of the Haber-Bosch process, developing economic and environmentally benign ammonia synthesis process has attracted great interests. This work focuses on the moderately high two-step solar water-splitting of VN to produce ammonia, thus avoiding the reliance of fossil-fuel based heating source and pure hydrogen. Based on the equilibrium composition analysis, we find that V₂O₃, CH₄ and N₂ with mole ratio of 1:3:1.5 at T_H = 1050 °C is enough for complete methane reforming and sufficient nitrogen fixation of V₂O₃. As for the water-splitting of VN, the production of NH₃ is only possible at T_L ≤ 400 °C, and inputting excessive water vapors is found to exert little effect on ammonia production at H₂O:AlN>3:2. At the temperature range of full conversion between V₂O₃ and VN, the cycle efficiency, η_cycle, and solar-to-fuel efficiency, η_{solar-to-fuel,} under different operating temperatures are compared, in which the highest η_cycle and η_{solar-to-fuel} are 31.9% and 35.3% respectively. Moreover, efficiencies could be increased up to more than 37% with consideration of heat recuperation, demonstrating the great solar energy storage and fuel production potential of the proposed system.